Jacketed fissionable member



Sept. 13, 19,60

E. R. BOLLER ET AL JACKETED FISSIONABLE MEMBER Filed May 5. 1947 INVENTORJI WMM Patented Sept. 13, 1960' 2,952,603 JACKETED FISSIONABLE NIEMBER Filed May 5, 1947, Ser. No. 746,026 2 Claims. (Cl. 204193.2)

Robinson,

This invention relates to an improved construction of a jacketed member of fissionable material. More specifically, the invention relates to yan improvement in the jacketing of iissionable materials such as uranium to prevent escape of iissionable material from the jacket and to prevent corrosion of the ssionable material when used in a neutronic reactor.

In neutronic reactors of any type, a neutron-ssionable isotope such as U233, U235, or Pu239 is subjected to ssion by neutron bombardment and a self-sustaining chain reaction is established by the neutrons evolved by the lission. The theory and operation of such reactors are described in the co-pending application of Enrico Fermi and Leo Szilard, Serial No. 568,904, led December 19, 1944, now Patent No. 2,708,656, dated May 17, 1955.

In the operation of such reactors at high power, difculty may be encountered due to elements of the reactor other than the issionable material becoming contaminated with radioactive fragments of ssionable material. Therefore, such reactors now commonly have the ssionable materials covered by non-fissionable jackets -which are sealed so that radioactive substances may not escape. When such jackets are employed, it becomes necessary, where high-temperature operation of the reactor is to be undertaken, to insure excellent heat transfer between the fissionable material, in which heat is generated, and the jacket, in order that the heat may be carried off. This is necessary both from the point of view of utilization of the heat and from the point of view of avoiding the development of excessively high temperatures within the ssionable material.

It has been found convenient to use the ssionable materials in the form of slugs which are commonly cylindrical in shape and of a length which renders their fabrication and use practical and convenient. Such slugs of iissionable material `are commonly placed end-to-end in the reactor in channels provided for lthis purpose. The reactor is provided with a liquid or gas coolant which is circulated past the jacketed slugs and carries olf the heat generated in the ssionable material and transmitted to the jacket material. The. jacket material is usually of high thermal conductivity and low neutron absorption, such as aluminum, and is commonly bonded to the fissionable material by a bonding layer of a suitable thermally conductive material.

Such jackets must be completely pressure-tight in order to prevent leakage of the coolant into the jacket and consequent corrosion, and likewise to prevent leakage of radioactive materials from the interior of the jacket into the coolant. It has been found that ordinary pressure-tight containers cannot sutficiently accomplish this purpose because of the extremely adverse conditions of temperature to which such jackets, as above described, are exposed. Therefore, it is necessary, to provide a jacket which constitutes an enclosure which is hermetic to an extent heretofore not known.

It is the principal object of this invention to provide a jacket for iissionable material adapted to maintain a ssionable material.

pressure-tight seal under the conditions neutronic reactor described above.

More specically, it Iis an object of this invention to provide an assembly of a issionable material within a protective jacket which minimizes the possibility of leakage between the exterior of the jacket and the flssionable material contained therein.

Generally speaking the above objects of this invention are achieved by maximizing the length of the potential leakage path from the exterior of the jacket to the The possibility of the development of leakage is greatest through the seal or bond which effects closure of the jacket. The present invention prevents such leakage by providing a structure in which leakage cannot be caused by development of slight defects in Ithe seal or bond. For a more complete understanding of the invention, reference is made to the attached drawing, in Which:

Figs. l, 2, and 3 are each longitudinal sectional views, shown partially in elevation, of jacketed cylindrical memoccurring in a Y bers of thermal neutron issionable material, each embodying the teachings of this invention.

Referring to all of the figures of the drawing, the numeral 10 designates a cylindrical body of fssionable material such as uranium. At each end of the issionable body 10 is a shoulder portion 12 of smaller diameter than the remainder of the body 10. At the extreme outer end of the shoulder portion is an annular flange 14. Over Ithe shoulder portion 12 is fitted a cup-shaped end cap 16 having an outer diameter corresponding to the outer diameter of the central portion of the body 10 and an inner diameter slightly larger than the outer diameter of the shoulder portion 12.

The end caps 16 have on the internal surfaces thereof grooves which cooperate with the annular flanges 14. The caps 16 are preferably bonded to the ssionable body 10 by a bonding layer 18 of a material of low neutron absorption, for example an aluminum-silicon alloy. The cap 16 is preferably of a material of high thermal conductivity and low neutron absorption such as aluminum. It will be understood 1that the thickness of the bonding layer 18 is exaggerated 4in the drawing for clarity.

It will be seen that the fissionable body 10, having over the ends thereof the end cap 16, constitutes a cylindrical assembly of substantially uniform diameter. The body 10 is surrounded by a cup-shaped jacket 20, preferably of aluminum, likewise exaggerated in thickness in the drawing. The jacket 20 is likewise bonded to the body 10 and to the caps 16 by a bonding layer 22, for example of an alloy of aluminum and silicon, similar to the bonding layer 18.

Within the open end of the cup-shaped jacket 20 is a closure disc 24, likewise preferably of aluminum and preferably bonded to the outer end cap 16 by a portion of the bonding layer 22. The sealing of the closure disc 24 to the open end of the cup-shaped jacket 20 to eifect closure thereof may be made, for example, by welding or, as illustrated in the drawing, the closure may be effected by the bonding layer 22.

The weakest portion of the jacket covering the lissionable body 10 as regards leakage is likely to be the seam between the closure cap 24 Iand the end of the cup-shaped jacket 20. In this past, the jacketed body 10 has been made uniform-in diameter. With such construction, any development of a fault in the seam 26 may immediately cause leakage between the iissionable body and the exterior, thus permitting both the escape of iissionable material from the jacket and the corrosion of the fissionable material, both of which effects are extremely undesirable in the operation of a neutronic reactor. In the present invention, as may be seen, it is necessary for leakage that a faultv develop not only in the seam 26 but along the entire portion of the bonding layer 22 lying along the wall of the outer end `cap 16. It will be seen that this effect is accomplished without -the addition of the substantial amounts of material non-fissionable by thermal neutrons which Would be required if the purpose of this invention were to be achieved by adding a. very thick closure disc 24 instead of employing the end cap 16, or by adding an additional outer jacket to the structure.

In addition to the advantages above stated, the provision of the end caps 16 permits ready assembly of such jacketed bodiescontaining devices for preventing the development of high temperatures at the ends'of the cylindrical bodies. As` stated above, the jacketed bodies or slugs offssionable material are commonly placed end-to-.end in the neutronc reactor. As is Well known, the fluid coolant which- Yis circulated past the jacketed slugs is relatively ineffective, in removing heat from the abutting Vend surfaces of adjoining slugs.y Therefore, precautions must be taken to preventfthe development of advantage described above, i.e., the simple assembly incorporating the insulating or conducting device for preventing high temperatures at the end of the jacket 20. It will be understood that -the end cap 16 may advantageously be used at the closure end of the body for the sole purpose of lengthening the Ileakage path as described above, in cases where the illustrated thermally conducting and insulating devices are not employed:v

The teachings of the invention shall notV be deemed to be limited to the embodiments illustrated'in the drawing and described above. Many. equivalent devices employing the teachings will readily be Ydevised by persons skilled in the art. Therefore, the present invention shall be deemed to be limitedL only by the appended claims.

What is claimed is:

1. As an article of manufacture, an elongated body comprising thermal neutron ssionable material having a shoulder portion at an end thereof, the shoulder having an annularange at the extreme outer end, a substanhot spots -at the inner surfaces between the jacketed slugs. Such precautions usually take one of two vforms. One device for accomplishing this purpose is to provide in the end of the jacket a lmass of material of high thermal conductivity so that-heat is quickly carried from the end surfacesito the side walls. Another device is the thermal insulation of the ends of the jacket from the fssionable body contained therein so that lall of the heatv generated within the jacket is conducted to the walls, rather than to the ends, thereof.

In the illustration Vof Fig. 1, there is placed within the top of the cup-shaped end cap 16 a thick disc 30, -o aluminum, which is bonded -to the end ofthe fissionable body 10 by a bonding layer 32 similar to the bonding layers 4described above. In this manner heat is conducted away `from the end por-tions to the wallsof the jacket.

In the embodiment of Fig. 2, there is placed wit/hin. the cup-shaped cap 1,6 a recessed disc 34, for example of iron or beryllium, back by a body 36 of aluminum. The recessin the disc 34'forms an airl gap 38 at the ends of the fissionable bodyY 10. The air gap 38 serves to insulate thermally the ends of the jacketed slug from the heat-generating tissionable body 10. In the embodiment of Fig. 3, there is iitted within the cup-shaped end cap 16 a small cup-shaped disc 40, for example of beryllium, the lipsv of the cup-shaped d-isc 40 resting against the ends of the jacketed body 10 and the cavity thus formed constituting an air gap 42- insulating the endsl of the jacket from the iissionable body 10.

Itwill be .noted that inthe illustrations of ltheY draw-ing the endy capsA 16 are employed at both ends of the jacketed' body 10. Obviously the end cap 16 at the end of the jackety 20 opposite the closure discr 24 does not serve to lengthen the leakage path between the exterior ofy the assembly and the issionable body 10 through the seam 26,` as does the end cap 16 at the end at which closure is made by the closure disc 24. The end cap 16 is employed in the former position because of the secondl tiallycup-shaped cap fitted over the shoulder, and having an annular groove on the internal surface alignable with the flange, a jacket having an open end and fitted over the body andthe cap and bonded to the cap overrtheir f entire interface by a Ybonding layer, and a closure disc sealed to the open end of the jacket, said open end of the jacket being at the end of the body having the cap,- and s-aidlayer, cap, disc and jacket comprising materials Voi low neutron absorption.

f 2. In combination, a cylinder of uranium having end portions of smaller diameter than that of the central portion and -having tiangesat the Vend thereof, two cupshap'ed end-caps of aluminum having an outer diameter v substantially the same as that of said center portion, said end-caps being adapted to t over said ends and having internal annular grooves adapted to receive said flanges, said end-caps'bei-ng adapted to prevent the concentration in said end-caps of'heat generated inthe uranium, a covering -jacket of aluminum having one open end, and a closure disc covering the open end of the jacket and being bonded Vto said open end and to an en-d cap said end-caps being bonded to the uranium andto said jacket over their entire interface, and saidv jacket being bonded to the structure thus formed by an alloy of aluminum and silicon.

References Cited in the le of this patent lUNITED STATES PATENTS OTHER REFERENCES Smyth: Atomic Energy lfor Military Purposes, pages 103, 104, August 1945. Copy may be purchased -from Supt. of Documents, Washington 25, D.C.

Kelly etal.: Physical Review 73, 1135-9 (1948). 

1. AS AN ARTICLE OF MANUFACTURE, AN ELONGATED BODY COMPRISING THERMAL NEUTRON FISSIONABLE MATERIAL HAVING A SHOULDER PORTION AT AN END THEREOF, THE SHOULDER HAVING AN ANNULAR FLANGE AT EXTREME OUTER END, A SUBSTANTIALLY CUP-SHAPED CAP FITTED OVER THE SHOULDER, AND HAVING AN ANNULAR GROOVE ON THE INTERNAL SURFACE ALIGNABLE WITH THE FLANGE, A JACKET HAVING AN OPEN END AND FITTED OVER 